1. Field of the Invention
The present invention relates to devices and methods for repairing bone fractures, and, more particularly, to intramedullary nails and related internal fixation methods especially suitable for repairing long-bone fractures in children.
2. Description of Related Art
The use of intramedullary nails in the repair of long-bone fractures, such as in the femur, has been known in the orthopedic field. Exemplary devices include those known as the Rush and Enders and the Kuntschner nails, as well as those disclosed in U.S. Pat. No. 5,713,902 to Friedl; U.S. Pat. No. 5,697,930 to Itoman et al.; U.S. Pat. No. 5,573,536 to Grosse et al.; U.S. Pat. No. 5,562,666 to Brumfield; U.S. Pat. No. 5,374,235 to Ahrens; U.S. Pat. No. 5,312,406 and U.S. Pat. No. 5,167,663 to Brumfield; U.S. Pat. No. 5,122,141 to Simpson; U.S. Pat. No. 5,066,296, U.S. Pat. No. 5,041,114, and U.S. Pat. No. 4,776,330 to Chapman et al.; U.S. Pat. No. 4,976,258 to Richter et al.; U.S. Pat. No. 4,875,475 to Comte et al.; U.S. Pat. No. 4,846,162 to Moehring; U.S. Pat. No. 4,506,662 to Anapliotis; and U.S. Pat. No. 4,475,545 to Ender.
Referring to FIG. 1, a special problem in pediatric orthopedics exists in that reaming through the typical entry point in a femur 10, i.e., the piriformis fossa 11, can be too dangerous for the child. This is due to the presence of an artery 12 that supplies blood to the proximal femur. Specifically, this is the lateral epiphyseal artery 12 which is a branch of the femoral artery. If this artery 12 is damaged during the fixation procedure, such as while the intramedullary canal is being reamed to accept a nail, or possibly during insertion or after insertion of the nail, various complications can result. The lateral epiphyseal artery 12 supplies 75% of the blood to the growing femoral head 16. If this artery 12 is damaged, then much of the femoral head 16 will die or necrose. The femoral head 16 will then heal with an irregular shape which inevitably leads to hip arthritis.
Various nails, such as flexible Rush nails, are non-interlocked meaning that cross fasteners are not used to secure the nail to the bone. These nails are often small diameter rods, on the order of approximately 3-4 mm in diameter. In addition to being flexible to a significant degree prior to plastic deformation, non-interlocked solid nails or rods can be relatively easily bent with plastic deformation to a desired shape. A plurality of these nails or rods are typically driven into the intramedullary canal depending on the support necessitated by the fracture and bone characteristics of the patient. Other more rigid solid or hollow nails are interlocked to the bone using cross fasteners typically at the proximal and distal ends of the nail. Unlike non-interlocked nails, interlocked nails require sufficient cross-sectional dimensions to accommodate holes necessary for the cross fasteners. Currently available interlocked nails can be inserted away from the lateral epiphyseal artery 12 but are so rigid that they migrate during insertion dangerously close to the artery 12 and can endanger it. In addition, the large proximal size of small adult interlocked nails, which have typically been used in children, increases the potential for damage to the growth plate 17 at the proximal femur.
Among possible solutions, retrograde nailing avoids the proximal femur but also has at least one potential problem. The nails must be introduced close to the distal femoral growth plate or physis 19 (FIG. 5) at an awkward angle, potentially causing growth arrest distally on the femur, i.e., adjacent the knee. An approach through the greater trochanter 18 is also well recognized, but usually only one small diameter non-interlocked nail or rod can be used because of the narrow safe entry zone of the greater trochanter. A second small diameter nail or rod needs to be inserted retrograde or through the opposite end of the femur in these situations. These small diameter, flexible nails allow flexure after insertion and the slightly added stress to the bone allowed by this flexure promotes faster bone healing. These non-interlocked nails work well for transverse fractures. However, spiral or comminuted fractures often need additional external support, such as with a cast or brace. This is due to the inability of the non-interlocked nail to effectively prevent rotation or length compromise at the fracture.
It would therefore be desirable to provide an interlocked intramedullary nail, especially suitable for pediatric use, which provides flexibility along a majority of the length of the nail to facilitate faster healing of a fracture, but which also provides for secure interlocking of the nail to the bone with cross fasteners to prevent compromising the fracture due to rotation or shortening at the fracture site. Ideally, such a nail and related methods of insertion would minimize trauma to the growth plates of the femur as well as the arteries that supply blood to the proximal end of the femur while still allowing easy insertion and fixation within the intramedullary canal.